Transcript Chapter_06

Chapter 6: The Importance of Cells
•
All organisms are made of cells
•
The cell is the simplest collection of matter that can support life
•
Cell structure is correlated to cellular function
•
All cells are related by their descent from earlier cells
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Cells are the key to life!
• Outline:
• A) How can we look at cells? Microscopes!
• B) How can we study the components of cells?
• C) Prokaryotic and Eukaryotic cell structure.
• D) External cellular structures
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To study cells, biologists use microscopes and the
tools of biochemistry
•
Though usually too small to be seen by the unaided eye, cells can be
extremely complex
•
Scientists use microscopes to visualize cells too small to see with the
naked eye
•
In a light microscope (LM), visible light passes through a specimen and
then through glass lenses, which magnify the image
•
The minimum resolution of an LM is about 200 nanometers (nm), the
size of a small bacterium
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10 m
Microscopy
Human height
Length of some
nerve and
muscle cells
0.1 m
Chicken egg
•Most subcellular
structures, or organelles,
are too small to be
resolved by a LM
Frog egg
1 mm
1 centimeter (cm) = 10–2 meter (m) = 0.4 inch 100 µm
1 millimeter (mm) = 10–3 m
1 micrometer (µm) = 10–3 mm = 10–6 m
1 nanometer (nm) = 10–3 µm = 10–9 m
10 µm
Most plant and
animal cells
Nucleus
Most bacteria
1 µm
100 nm
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
10 nm
Proteins
Lipids
1 nm
Small molecules
0.1 nm
Atoms
Electron microscope
•Various techniques
enhance contrast and
enable cell components
to be stained or labeled
1 cm
Light microscope
•LMs can magnify
effectively to about 1,000
times the size of the
actual specimen
Measurements
Unaided eye
1m
A compound, optical microscope is most commonly used in teaching
and research laboratories.
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Brightfield (unstained
specimen)
Techniques to
enhance contrast:
Staining
50 µm
Brightfield (stained
specimen)
Phase-contrast
Differentialinterferencecontrast (Nomarski)
Techniques to
enhance contrast:
Labeling some
cellular components
for visualization
Fluorescence
50 µm
Confocal
https://www.youtube.com/watch
?v=qvGVoxdy-yM
50 µm
Electron microscopes are used to study the VERY SMALL
1 µm
organelles of a cell, or other small particles
Cilia
•
Two basic types of electron
microscopes (EMs) are used to
study subcellular structures
•
Scanning electron microscopes
(SEMs) focus a beam of electrons
onto the surface of a specimen,
providing images that look 3D
•
Transmission electron
microscopes (TEMs) focus a
beam of electrons through a
specimen
•
TEMs are used mainly to study
the internal ultrastructure of cells
Scanning electron
microscopy (SEM)
Transmission electron
microscopy (TEM)
Longitudinal
section of
cilium
Cross section
of cilium 1 µm
Comparison of optical and electron microscopes.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Questions:
•
What types of microscopes would you use if you would like to visualize
the following structures:
–
A. A human (eukaryotic) cell?
–
B. A bacterial (prokaryotic) cell?
–
C. A virus?
–
D. A plant (eukaryotic) cell?
–
E. An organelle of a cell?
–
F. A protein?
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Studying cells by biochemical techniques: Isolating
Organelles by Cell Fractionation
•
Cell fractionation takes cells apart and separates the major organelles
from one another
•
Ultracentrifuges fractionate cells into their component parts
•
Cell fractionation enables scientists to determine the functions of
organelles
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Isolating Organelles by Cell Fractionation
Homogenization
Tissue
cells
Differential centrifugation
Homogenate
Ultracentrifuges are used
To fractionate the organelles
From a cellular extract
1000 g
(1000 times the
force of gravity)
10 min
Supernatant poured
into next tube
bucket
with tube
20,000 g
20 min
80,000 g
60 min
Pellet rich in
nuclei and
cellular debris
150,000 g
3 hr
rotor
with buckets
centrifuge
Pellet rich in
mitochondria
(and chloroplasts if cells
are from a plant)
Pellet rich in
“microsomes”
(pieces of plasma
membranes and
cells’ internal
membranes)
Pellet rich in
ribosomes
Eukaryotic cells have internal membranes that
compartmentalize their functions
•
The basic structural and functional unit of every organism is one of two
types of cells: prokaryotic or eukaryotic
•
Only organisms of the domains Bacteria and Archaea consist of
prokaryotic cells
•
Protists, fungi, animals, and plants all consist of eukaryotic cells
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Comparing Prokaryotic and Eukaryotic Cells
•
Basic features of all cells (both prokaryotic and eukaryotic cells):
–
Plasma membrane
–
Semifluid substance called the cytosol
–
Chromosomes (carry genes)
–
Ribosomes (make proteins)
•
Prokaryotic cells have no nucleus
•
In a prokaryotic cell, DNA is in an unbound region called the nucleoid
•
Prokaryotic cells lack membrane-bound organelles
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An example of a prokaryotic cell
Pili
Nucleoid
Ribosomes
Plasma
membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 µm
Flagella
A typical
rod-shaped
bacterium
A thin section through the
bacterium Bacillus
coagulans (TEM)
Eukaryotic cells
•
Eukaryotic cells have DNA in a nucleus that is bounded by a
membranous nuclear envelope
•
Eukaryotic cells have membrane-bound organelles
•
Eukaryotic cells are generally much larger than prokaryotic cells
•
The logistics of carrying out cellular metabolism sets limits on the size
of cells
•
The plasma membrane is a selective barrier that allows sufficient
passage of oxygen, nutrients, and waste to service the volume of the
cell
•
The general structure of a biological membrane is a double layer of
phospholipids
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Plasma Membranes surround the cell
Outside of cell
Carbohydrate side chain
Hydrophilic
region
Inside of cell 0.1 µm
Hydrophobic
region
Hydrophilic
region
TEM of a plasma membrane
Phospholipid
Proteins
Structure of the plasma membrane
A Panoramic View of the Eukaryotic Cell
• A eukaryotic cell has internal membranes that partition the
cell into organelles
• Plant and animal cells have most of the same organelles
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An animal cell
In animal cells
but not plant
cells: Lysosomes
Centrioles
Flagella (in some
plant sperm)
A plant cell
In plant cells but not
animal cells:
Chloroplasts
Central vacuole and
tonoplast
Cell wall
Plasmodesmata
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The eukaryotic cell’s genetic instructions are housed in the
nucleus and carried out by the ribosomes
•
The nucleus contains most of the DNA in a eukaryotic cell
•
Ribosomes use the information from the DNA to make proteins
•
The nucleus contains most of the cell’s genes and is usually the most
conspicuous organelle
•
The nuclear envelope encloses the nucleus, separating it from the
cytoplasm
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The eukaryotic cellular nucleus houses the DNA
genome
of the cell
Nucleus
Nucleus
1 µm
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Pore
complex
Rough ER
Surface of nuclear envelope
Ribosome
1 µm
0.25 µm
Close-up of nuclear
envelope
Pore complexes (TEM)
Nuclear lamina (TEM)
Ribosomes: Protein Factories in the Cell
•
Ribosomes are particles made of ribosomal RNA and protein
•
Ribosomes carry out protein synthesis in two locations:
–
In the cytosol (free ribosomes)
–
On the outside of the endoplasmic reticulum (ER) or the nuclear
envelope (bound ribosomes)
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Ribosomes: Protein Factories in the Cell
Ribosomes
ER
Cytosol
Endoplasmic
reticulum (ER)
Free ribosomes
Bound ribosomes
Large
subunit
Small
subunit
0.5 µm
TEM showing ER
and ribosomes
Diagram of
a ribosome
The endomembrane system regulates protein traffic and
performs metabolic functions in the cell
•
•
Components of the endomembrane system – which are regions of the
cell that are composed of a membrane that transport things between
different compartments of a cell:
–
Nuclear envelope – surrounds the nucleus
–
Endoplasmic reticulum
–
Golgi apparatus
–
Lysosomes
–
Vacuoles
–
Vesicles
–
Plasma membrane – encases the entire cell and contains the
cytoplasm holding all of the organelles
These components are either continuous or connected via transfer by
vesicles
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Endomembrane System
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The Endoplasmic Reticulum: Biosynthetic Factory
•
The endoplasmic reticulum (ER) accounts for more than half of the total
membrane in many eukaryotic cells
•
The ER membrane is continuous with the nuclear envelope
•
There are two distinct regions of ER:
–
–
Smooth ER, which lacks ribosomes
•
Synthesizes lipids
•
Metabolizes carbohydrates
•
Stores calcium
•
Detoxifies poison
Rough ER, with ribosomes binding to and studding its surface
•
Produces proteins and membranes, which are distributed by transport
vesicles
•
Is a membrane factory for the cell
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Smooth ER
The Endoplasmic
Reticulum:
biosynthetic
factory
Rough ER
Nuclear
envelope
ER lumen
Cisternae
Ribosomes
Transport vesicle
Smooth ER
Transitional ER
Rough ER
200 nm
The Golgi Apparatus: Shipping and
Receiving Center
•
The Golgi apparatus consists of flattened membranous sacs called
cisternae
•
Functions of the Golgi apparatus:
–
Modifies products of the ER
–
Many post-translational modifications to proteins are performed in
the cisternae of the Golgi
–
Manufactures certain macromolecules
–
Sorts and packages materials into transport vesicles
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The Golgi Apparatus: Shipping and
Receiving Center
Golgi
apparatus
cis face
(“receiving” side of
Golgi apparatus)
Vesicles also
transport certain
proteins back to ER
Vesicles move
from ER to Golgi
Vesicles coalesce to
form new cis Golgi cisternae
0.1 µm
Cisternae
Cisternal
maturation:
Golgi cisternae
move in a cisto-trans
direction
Vesicles form and
leave Golgi, carrying
specific proteins to
other locations or to
the plasma membrane for secretion
Vesicles transport specific
proteins backward to newer
Golgi cisternae
trans face
(“shipping” side of
Golgi apparatus)
TEM of Golgi apparatus
Lysosomes: Digestive Compartments
•
A lysosome is a membranous sac of hydrolytic enzymes
•
Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and
nucleic acids
•
Lysosomes can digest material taken into the cell from outside by a
process know as phagocytosis
•
Lysosomes also use enzymes to recycle organelles and
macromolecules from within the cell, a process called autophagy
•
Plant cells do not have lysosomes
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1 µm
Nucleus
Lysosomes:
digestive
compartments
within the cell
Phagocytosis
Lysosome
Lysosome contains Food vacuole Hydrolytic
active hydrolytic
enzymes digest
fuses with
enzymes
food particles
lysosome
Digestive
enzymes
Plasma
membrane
Lysosome
Digestion
Food vacuole
Phagocytosis: lysosome digesting food
Lysosome containing
two damaged organelles
Lysosomes:
digestive
compartments
within the cell
1 µm
Mitochondrion
fragment
Peroxisome
fragment
Autophagy
Lysosome fuses with
vesicle containing
damaged organelle
Hydrolytic enzymes
digest organelle
components
Lysosome
Digestion
Vesicle containing
damaged mitochondrion
Autophagy: lysosome breaking down
damaged organelle
Vacuoles: Diverse Maintenance Compartments
•
Vacuoles are membrane-bound sacs with varied functions
•
A plant cell or fungal cell may have one or several vacuoles
•
Food vacuoles are formed by phagocytosis
•
Contractile vacuoles, found in many freshwater protists, pump excess
water out of cells
•
Central vacuoles, found in many mature plant cells, hold organic
compounds and water
•
Animal cells do not have central vacuoles
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Vacuoles: Diverse Maintenance Compartments
Central vacuole
Cytosol
Tonoplast
Nucleus
Central
vacuole
Cell wall
Chloroplast
5 µm
Vesicles perform many different intracellular
functions
•
Vesicles, like vacuoles, are membrane-bound sacs with varied
functions
•
They are much smaller than vacuoles
•
The perform many functions within the cell, including moving material
between the ER and Golgi and moving things between the cisternae of
the Golgi
•
They also function in delivering things into the cell from the
extracellular environment in a process known as endocytosis
•
They also deliver things to be excreted such as waste and hormones to
the exterior of the cell in a process known as exocytosis
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A diagram of how things are transported out of a cell by vesicle
movement
Nucleus
Rough ER
Smooth ER
Nuclear envelope
cis Golgi
Transport vesicle
Plasma
membrane
trans Golgi
Work in groups and try to put these cellular processes in order
for a protein destined for secretion
•
A piece of mRNA is synthesized by transcription from a DNA gene
•
A vesicle containing a protein fuses with the plasma membrane to
release the protein out of the cell
•
The ribosome synthesizes a protein by translation
•
The protein enters into the endoplasmic reticulum (ER) to be modified
•
The protein is folded to form secondary protein structures
•
The protein first enters into a vesicle
•
The protein is folded to form tertiary and quaternary protein structures
•
The protein enters into the cis Golgi apparatus for modifications
•
The protein leaves the Golgi apparatus in a vesicle
•
The protein is transported in transport vesicles between the cisternae
of the Golgi apparatus
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Mitochondria and chloroplasts change energy
from one form to another
•
Mitochondria are the sites of cellular respiration
•
Chloroplasts, found only in plants and algae, are the sites of
photosynthesis
•
Mitochondria and chloroplasts are not part of the endomembrane
system
•
Peroxisomes are oxidative organelles
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Mitochondria: Chemical Energy Conversion
•
Mitochondria are in nearly all eukaryotic cells
•
They have a smooth outer membrane and an inner membrane folded
into cristae
•
The inner membrane creates two compartments: intermembrane
space and mitochondrial matrix
•
Some metabolic steps of cellular respiration are catalyzed in the
mitochondrial matrix
•
Cristae present a large surface area for enzymes that synthesize ATP
as the final steps of cellular respiration
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Mitochondria: Chemical Energy Conversion
Mitochondrion
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
Mitochondrial
DNA
100 nm
Chloroplasts: Capture of Light Energy
•
The chloroplast is a member of a family of organelles called plastids
•
Chloroplasts contain the green pigment chlorophyll, as well as
enzymes and other molecules that function in photosynthesis
•
Chloroplasts are found in leaves and other green organs of plants and
in algae ANIMALS DO NOT HAVE CHLOROPLASTS
•
Chloroplast structure includes:
–
Thylakoids, membranous sacs
–
Stroma, the internal fluid
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Chloroplasts: Capture of Light Energy
Chloroplast
Ribosomes
Stroma
Chloroplast
DNA
Inner and outer
membranes
Granum
1 µm
Thylakoid
Peroxisomes: Oxidation
•
Peroxisomes are specialized metabolic compartments bounded by a
single membrane
•
Peroxisomes produce hydrogen peroxide and convert it to water
Chloroplast
Peroxisome
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Mitochondrion
The cytoskeleton is a network of fibers that organizes
structures and activities in the cell
•
The cytoskeleton is a network of fibers extending throughout the
cytoplasm
•
It organizes the cell’s structures and activities, anchoring many
organelles
•
It is composed of three types of molecular structures:
–
Microtubules
–
Microfilaments
–
Intermediate filaments
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The cytoskeleton is a network of fibers that
organizes structures and activities in the cell
Microtubule
Microfilaments
0.25 µm
Roles of the Cytoskeleton: Support, Motility, and Regulation
•
The cytoskeleton helps to support the cell and maintain its shape
•
It interacts with motor proteins to produce motility
•
Inside the cell, vesicles can travel along “monorails” provided by the
cytoskeleton
•
Recent evidence suggests that the cytoskeleton may help regulate
biochemical activities
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The role of the cytoskeleton in intracellular
vesicle movement
Vesicle
ATP
Receptor for
motor protein
Motor protein
(ATP powered)
Microtubule
of cytoskeleton
An EM image of vesicles being transported
Along a microtubule (the cytoskeleton)
Microtubule
Vesicles
0.25 µm
Components of the Cytoskeleton
•
Microtubules are the thickest of the three components of the
cytoskeleton
•
Microfilaments, also called actin filaments, are the thinnest
components
•
Intermediate filaments are fibers with diameters in a middle range
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Components of the Cytoskeleton: Microtubules
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Microtubules:
Centrosomes and
Centrioles
•In many cells, microtubules
grow out from a centrosome
near the nucleus
Centrosome
Microtubule
Centrioles
0.25 µm
•The centrosome is a
“microtubule-organizing
center”
•In animal cells, the
centrosome has a pair of
centrioles, each with nine
triplets of microtubules
arranged in a ring
Longitudinal section Microtubules
of one centriole
Cross section
of the other centriole
Microtubules: Cilia and Flagella
•
Microtubules control the beating of cilia and flagella, which are the
locomotor appendages of some cells
•
Cilia and flagella share a common ultrastructure:
–
A core of microtubules sheathed by the plasma membrane
–
A basal body that anchors the cilium or flagellum
–
A motor protein called dynein, which drives the bending
movements of a cilium or flagellum
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Structure of Flagella and cilia
Outer microtubule
doublet
Dynein arms
Central
microtubule
0.1 µm
Cross-linking
proteins inside
outer doublets
Microtubules
Plasma
membrane
Basal body
0.5 µm
Radial
spoke
0.1 µm
Triplet
Cross section of basal body
Plasma
membrane
Microtubule
doublets
Flagella and
Cilia movements
via dynein
Dynein arms
alternately grab,
move, and
release
the outer
microtubules
such
that dynein
appears
to be “walking”
and
pulling one
microtubule past
another.
Dynein “walking”
ATP
Dynein arm
Flagella and
Cilia movements
via dynein
•Protein cross-links limit
sliding
and holds doublets of
microtubules together
Cross-linking
proteins inside
outer doublets
Anchorage
in cell
Effect of cross-linking proteins
•Forces exerted by
dynein arms cause
doublets to curve,
bending the cilium or
flagellum
Wavelike motion
ATP
Cilia and Flagella differ in their beating pattern
FLAGELLA
Direction of swimming
Motion of flagella
5 µm
Cilia and Flagella differ in their beating pattern
Cilia
Direction of organism’s movement
Direction of
active stroke
Motion of cilia
Direction of
recovery stroke
15 µm
Components of the Cytoskeleton: Microfilaments
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Microfilaments (Actin Filaments)
•
Microfilaments are solid rods about 7 nm in diameter, built as a twisted
double chain of actin subunits
•
The structural role of microfilaments is to bear tension, resisting pulling
forces within the cell
•
They form a 3D network just inside the plasma membrane to help
support the cell’s shape
•
Bundles of microfilaments make up the core of microvilli of intestinal
cells
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Microvilli in
intestinal cells
are made of
microfilaments
Microvillus
Plasma membrane
Microfilaments (actin
filaments)
Intermediate filaments
0.25 µm
Microfilaments (Actin Filaments) in muscle cells
•Microfilaments that function in cellular motility contain the protein myosin in
addition to actin
•In muscle cells, thousands of actin filaments are arranged parallel to one another
•Thicker filaments composed of myosin interdigitate with the thinner actin fibers
Muscle cell
Actin filament
Myosin filament
Myosin arm
Myosin motors in muscle cell contraction
Microfilaments (Actin Filaments) in amoeba
movement
•Localized contraction brought about by actin and myosin also drives amoeboid
movement
•Pseudopodia (cellular extensions) extend and contract through the reversible
assembly and contraction of actin subunits into microfilaments
Cortex (outer cytoplasm):
gel with actin network
Inner cytoplasm: sol
with actin subunits
Extending
pseudopodium
Amoeboid movement
Microfilaments (Actin Filaments) in cytoplasmic
movement
•Cytoplasmic streaming is a circular flow of cytoplasm within cells
•This streaming speeds distribution of materials within the cell
•In plant cells, actin-myosin interactions and sol-gel transformations
drive cytoplasmic streaming
Nonmoving
cytoplasm (gel)
Chloroplast
Streaming
cytoplasm
(sol)
Vacuole
Parallel actin
filaments
Cytoplasmic streaming in plant cells
Cell wall
Components of the Cytoskeleton: Intermediate
Filaments
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Intermediate Filaments
•
Intermediate filaments range in diameter from 8–12 nanometers, larger
than microfilaments but smaller than microtubules
•
They support cell shape and fix organelles in place
•
Intermediate filaments are more permanent cytoskeleton fixtures than
the other two classes
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An animal cell
ENDOPLASMIC RETICULUM (ER
Nuclear envelope
Flagellum
Rough ER
Smooth ER
NUCLEUS
Nucleolus
Chromatin
In animal cells but
not plant cells:
Lysosomes
Centrioles
Flagella (in some
plant sperm)
Centrosome
Plasma membrane
CYTOSKELETON
Microfilaments
Intermediate filaments
Microtubules
Ribosomes:
Microvilli
Golgi apparatus
Peroxisome
Mitochondrion
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Lysosome
A plant cell
Nuclear
envelope
NUCLEUS
Nucleolus
Chromatin
Centrosome
Rough
endoplasmic
reticulum
Smooth
endoplasmic
reticulum
Ribosomes
(small brown dots)
In plant cells but not animal cells:
Chloroplasts
Central vacuole and tonoplast
Cell wall
Plasmodesmata
Central vacuole
Golgi
apparatus
Microfilaments
Intermediate
filaments
Microtubules
Mitochondrion
Peroxisome
Chloroplast
Plasma
membrane
Cell wall
Plasmodesmata
Wall of adjacent cell
CYTOSKELETON
Extracellular components and connections between cells
help coordinate cellular activities
•
Most cells synthesize and secrete materials that are to be released to
the external sides of the plasma membrane
•
These extracellular structures include:
–
Cell walls of plants
–
The extracellular matrix (ECM) of animal cells
–
Intercellular junctions
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Cell Walls of Plants
•
The cell wall is an extracellular structure that distinguishes plant cells
from animal cells
•
The cell wall protects the plant cell, maintains its shape, and prevents
excessive uptake of water
•
Plant cell walls are made of cellulose fibers embedded in other
polysaccharides and protein
•
Plant cell walls may have multiple layers:
•
–
Primary cell wall: relatively thin and flexible
–
Middle lamella: thin layer between primary walls of adjacent cells
–
Secondary cell wall (in some cells): added between the plasma
membrane and the primary cell wall
Plasmodesmata are channels between adjacent plant cells
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Central
vacuole
of cell
Cell Walls of Plants
Plasma
membrane
Secondary
cell wall
Primary
cell wall
Central
vacuole
of cell
Middle
lamella
1 µm
Central vacuole
Cytosol
Plasma membrane
Plant cell walls
Plasmodesmata
The Extracellular Matrix (ECM) of Animal Cells
•
Animal cells lack cell walls but are covered by an elaborate
extracellular matrix (ECM)
•
The ECM is made up of glycoproteins and other macromolecules
•
Functions of the ECM:
–
–
–
–
Support
Adhesion
Movement
Regulation
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The Extracellular Matrix (ECM) of Animal Cells
Collagen
fiber
EXTRACELLULAR FLUID
Fibronectin
Plasma
membrane
Integrin
CYTOPLASM
Microfilaments
Proteoglycan
complex
Proteoglycan
complex
The Extracellular
Matrix (ECM)
of Animal Cells
Polysaccharide
molecule
Carbohydrates
Core
protein
Proteoglycan
molecule
Intercellular Junctions
•
Neighboring cells in tissues, organs, or organ systems often adhere,
interact, and communicate through direct physical contact
•
Intercellular junctions facilitate this contact
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Intercellular junctions in Plants: Plasmodesmata
•
Plasmodesmata are channels that perforate plant cell walls
•
Through plasmodesmata, water and small solutes (and sometimes
proteins and RNA) can pass from cell to cell
Cell walls
Interior
of cell
Interior
of cell
0.5 µm
Plasmodesmata
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Plasma membranes
Intercellular junctions in Animals: Tight Junctions,
Desmosomes, and Gap Junctions
•
At tight junctions, membranes of neighboring cells are pressed
together, preventing leakage of extracellular fluid
•
Desmosomes (anchoring junctions) fasten cells together into strong
sheets
•
Gap junctions (communicating junctions) provide cytoplasmic
channels between adjacent cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Intercellular junctions
Tight junctions prevent
in Animals:
fluid from moving
across a layer of cells
Tight Junctions,
Desmosomes, and
Gap Junctions
Tight junction
0.5 µm
Tight junction
Intermediate
filaments
Desmosome
1 µm
Space
between
cells
Gap
junctions
Plasma membranes
of adjacent cells
Gap junction
Extracellular
matrix
0.1 µm
The Cell: A Living Unit Greater Than the Sum of Its Parts
•
Cells rely on the integration of all of the different structures and
organelles in order to function
•
For example, a macrophage’s ability to destroy bacteria involves the
whole cell, coordinating components such as the cytoskeleton,
lysosomes, and plasma membrane
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings